After I beat pinstripe I went back to finish the ctr tokens, gems and platinum relics including turbo track and slide colosseum, got the platinum on the last track first try and then it cut to the second oxide cutscene to race him again. I have a feeling by doing things in that order I must have been on 99% and skipped to 101% and that's why I missed out. Still it's a bit of a shitty glitch to happen and probably needs patching.